Definition
Aircraft piston engines that dissipate the heat produced by combustion directly into the surrounding air, rather than through a liquid coolant system. Cooling is achieved by routing outside air across finned cylinder barrels and heads, with baffles and cowl flaps directing and regulating airflow.
Plain English
Engines that are kept from overheating by airflow passing over them, instead of by liquid coolant like a car engine.
Context Anchor
Seen in engine starting, hand propping, preflight inspection, and ground operation discussions, especially on many small training airplanes.
Why Pilots Care
Pilots must understand cooling limits during ground operations such as hand propping, where low airflow can allow cylinder temperatures to rise quickly.
Grounding Statement
Picture the engine running on the ground after start: the metal parts are making heat, and the moving air around them is what carries that heat away.
Intuition Check
Air-cooled does not mean the engine is cooled just because it is outdoors. It means the engine depends on moving air over its hot parts to carry heat away.
Example Sentence 1
Because the trainer has an air-cooled engine, the instructor kept ground run-up time short to avoid overheating the cylinders.
Example Sentence 2
Most light trainers use air-cooled engines, which is why hand propping remains a practical starting method on many of these aircraft.